The camera says I need to format my memory card and when I do so the screen reads Filesys errore00100, how can I fix this?

Did you format the card using the camera's format feature (located in the menus) and NOT by formatting in the computer? Also, if this is a brand new card, make sure that you purchased a 2 GB or less STANDARD SD card, and NOT a 4GB or higher SDHC card. Your camera was manufactured before the newer SDHC format came out. Unfortunately there's no way that the SDHC format cards will work with your camera. If the previous did not apply to your situation, additional troubleshooting tips may be found at this link.

The card may be incompatible.

Memory cards have grown enormously in capacity in the last couple of years, and even relatively new cameras may not be able to cope with the memory size of the newest cards.

SD and SDHC cards fit the same slots, but many cameras won't work with the SDHC (high capacity) cards. SDHC is not backwards compatible.